This combination of physical properties becomes important and is useful in reinforcement of plastic laminates when lightweight, high strength construction is needed. Glass fibers produced from the glass compositions of this invention meet this criteria and find use in the aircraft industry and particularly in reinforced materials used in the construction of missiles, rockets, rocket motor covers, satellites, and other space and deep submergence vehicles and watercraft.

Commercial filament E-glass and S-glass are typical of fibers possessing high tensile strengths which are used as reinforcement for plastic and resin laminated structures. E-glass has a virgin glass fiber tensile strength of 500,000 p.s.i. and a virgin fiber density of 2.54 g./cc. S-glass has a virgin glass fiber order to form fibers at a specific viscosity, the range of available temperatures is very small. By adding magnesia to beryllia glasses, the viscosity-temperature curve is flattened, thereby widening the range of temperatures (at forming) for a more economical operation. Magnesia also reduces the tendency of these compositions to separate into two or more phases upon cooling.

The use of beryllia in glasses of the type described yields improved properties in the fibers produced therefrom. Said fibers exhibit high modulus of elasticity and low density.

Glasses of high Young's modulus are obtained when the interstices of a silicate network are filled with ions of high field strength. Beryllium is characterized as such an ion. Previous investigation has shown that such glasses are characterized by a low content of network formers, including silica and alumina. Compared on a cation-for-cation basis, beryllium is one of the most effective ions in raising the Young's modulus.

Below is a comparison of the ionic size and field strength of tensile strength of 700,000 p.s.i. and a virgin fiber density of beryllium, magnesium and calcium:

2.49 g./cc. The use of the term virgin" herein denotes that no sizing or after-treatment has been applied to said fiber.

It is one object of this invention to provide glass compositions that are commercially fiberizable and wherein fibers therefrom have high tensile strength, high modulus, high temperature resistance, and low density.

It is another object of this invention to provide glass compositions comprising SiO,, A1 0 MgO and BeO, that are commercially fiberizable wherein fibers therefrom are capable of withstanding high temperatures without materially chang- 3 ing composition or form during their useful life or without substantial loss in properties.

It is a further object to provide a glass composition that has exceptionally good fiberizable characteristics and wherein fibers therefrom possess a highly reactive surface that is readily compatible with protective compositions such as sizes, lubricants, finishes, various after treatments and the like.

Other objects and advantages will be apparent from the following description.

The components of the glass composition are present in the following proportions, expressed in mole percent. The preferred ranges of proportions for each constituent are as follows:

This range of proportions for each constituent was selected Because beryllium is so small in ionic size and possesses such a high field strength, glass compositions containing this 0 element have enhanced devitrification and phase separation carefully controlled conditions to obtain homogeneity before fiber forming.

Commercially, one method and apparatus by which the glasses of this invention may be melted under carefully controlled conditions to obtain a homogeneous melt is described in US. Pat. No. 3,264,076. Good quality fibers possessing 5 tion are formed into multifilament strands, yarns and roving by conventional methods and woven into fabric form for use alone or in laminated structures.

Glass compositions were prepared and samples tested as indicated in the following examples, wherein the ingredients were proportioned by mole percent. Although specific compositions have been disclosed, variations and modifications can be made within the spirit and scope of the invention.

only afteradetailed study had been undertaken and evaluated The glass compositions were melted from batch and for obtaining a glass composition which possessed good -fiberized by passing the molten glass through a plurality of orifiberizing characteristics, and which fibers therefrom possessed high tensile strength, high modulus, high temperature resistance and low density. Magnesia was found to be the only one of many oxides that contributed to lowering the viscosity fices of a precious metal bushing maintained at a temperature of about 2,9-00 F. to produce fibers of approximately 0.00025-0.00045 inches in diameter. Examination of the data in Table I shows that Examples l-Vlll are glass compositions and temperature of the glass of this invention, while maintainwithin the range of this invention. Although some of the proing good modulus and tensile properties on fibers pulled therefrom.

Glass compositions of the type described, without magnesia, are found to possess a steep viscosity-temperature curve, which on a production basis is not advantageous, because in perties of the glass compositions of these examples do not match the face value properties of Control A and Control B, the overall properties thereof hereinafter described in more detail are superior to those of the latter.

For example, one or two of the properties in question may not match the properties of Control A or Control B, but the third property is far superior to that of the controls. This property that is far superior shows up appreciably when all of the properties are evaluated together.

poises, at the temperature at which the fibers are formed, in order to facilitate continuous formation of fibers. The glass compositions are brought to a temperature sufficiently above the liquidus to insure that devitrification will not occur during 1 1 f a i i alumina beryllia magnesia type the fiber-forming. Heat removal from the glass during the the most important single factor in raising the Young's modufiber-forming is controlled y use of lus while maintaining low density, isthe addition of beryllia. lt' disposed ahmlt the orifices through which the mollch B has been determined b previous investigation that only in emits as a stream, see Russell Re. 24,060. The removal of heat beryllia glass compositions does the density decrease, whereas y cooling devices is in addifim the p other cations, such as calcium and magnesium increase the 10 Present in fiber-forming Processes becfmse of the density of glass compositions. This factor of low density is not rapid inci'em in h sulfa volum relatbhshil a natural, inherent characteristic, since the density of berylliwhlchfakes P 96 m the glass as it fibenzed. um (1.85 g./cc.) is higher than that of calcium (1.415 g./cc.) various f f f and nations may be made um and magnesium (1.740 g./cc.) but is dependent upon the role Invent)? f 3mm and appended clams which the beryllium ion plays in the structure. at 18 cialmed 1s: i

Because of their low density the glasses of this invention in- A P comlimng of hemmly have a specific tensile strength and specific modulus s1 l1ca, alumina, magnesm and beryllia that yields high strength, of elasticity greater than that of E-glass and in most examples hlgh modulus and huh inpemmrc tt fibers where? greater than that of 511m. one method for relating or defim 20 the mole percentages of said glass composition are as follows. ing the specific tensile strength and specific modulus of elasticity is by the following formulae: ggjfi'g 2. Specific Modulus-=Y/p MgO 1.0-1s.o wherein TS=tensile strength measure in p.s.i.

Y=n dulu3 f l m i measured i i 2. A glass composition as described in claim 1 wherein the p=density, measured in no./in. mole percentages of each constituent are as follows:

Following is a table showing the specific tensile strengths and specific moduli for E-glass, S-glass and some of the glasses 673 of this invention. Also included in the table is a column show- 2:8 :2; ing the product of specific tensile strength and specific modumo 3:9

in the above table, the ratio of TS/p is used to denote the 3. A glass composition as described in claim 1 wherein the high strength to weight relationship. Y/p is used to denote the mole percentages of each constituent are as follows: high bending or flex to weight relationship. The product of TS/pX Y/p is used by testing laboratories as another criteria for SiO, 65.0 rating different glass compositions that find use in applications where high strength, high modulus, low density reinforcea; ments are required.

f 'f' glass 'f'" of 1' P 4. A glass composition as described in claim 1 wherein the non find part1cular utility 1n plastic matricies as a reinforcing mole percentages of each Constituent are as follows: medium, either in continuous form as strand, yarn, roving, fabric, and woven roving, or in discontinuous form as chopped 600 strand and chopped strand mat. H5

The glasses of this invention melt readily in existing com- M I51) mercial glass-melting units. Commercial fiber-forming processes comprise the ste s of flowin a stream of molten glass from a melting source and attenu ting said stream into A glass composmon as defcnbed m clam l wherem the fibers by mechanically pulling the Stream through a plurality mole percentages of each constituent are as follows: of orifices in a "bushing" with a pulling device. As the glass is attenuated, solidification takes place and fine-diameter fibers ifs 'g'g are produced. Collet winders (U.S. Pat. No. 2,391,870) and 5 pulling wheels (U.S. Pat. No. 2,729,027) are used as devices 3 for mechanically attenuating fibers.

Certain glass compositions are difficult to fiberize because A 81583 p as described in claim 1 wherein the of their rapid devitrification rate at or near the liquidus temmole Percentages Ofeach consume! are as follows? perature, i.e. the point at which glass begins to crystallize. The liquidus temperature, for the glasses of this invention is about 2,785 F. Because of their viscosity-liquidus relationship, it 3:8 2'2 has been found desirable to have a viscosity of from -300 75 M30 i,

7. A glass composition as described in claim 1 wherein the mole percentages of each constituent are as follows:

SD, 70.0 Alp, 15.0 800 5.0 M30 10.0

8. A glass composition as described in claim 1 wherein the mole percentages of each constituent are as follows:

sio, 70.0 ALO, 15.0 BeO 2.5 M30 12.5

9. A glass composition as described in claim 1 wherein the mole percentages of each constituent are as follows:

SD 68.6 Al 12.: 8:0 11.: M30 2.0

14. Glass fibers formed from the glass composition of claim 5.

15. Glass fibers formed from the glass composition of claim 6.

V 16. Glass fibers formed from the glass composition of claim 7.

17. Glass fibers formed from the glass composition of claim 8.

18. Glass fibers formed from the glass composition of claim 9.

19. A multifilament strand of glass fibers formed from a glass composition wherein the range of mole percentages of each constituent consists essentially of:

a. 550-810 of SiO b. -180 ofAl O c. l.025.0 of BeO, and

d. l.0-15.0 of MgO.

20. A high temperature resistant fabric made of interwoven yarns, said yarns consisting essentially of glass fibers having high tensile strength, high modulus and low density comprising in mole percentages 55.0-82.0% SiO 8.0-l8.0% Al O l.025.0% BeO and l.015.0% MgO.